Synthetic films having a high permeability to gases such as oxygen, and moisture can be useful in many applications. Typically, ethylene acid copolymers are not known for high water/gas permeability. However, ethylene acid copolymers and/or their ionomers have other properties that would make them desirable in applications where water/gas permeability is an important factor.
One application where it can be desirable to have an ethylene acid copolymer with high water/gas permeability is as a casing for foodstuffs, or in food packaging. Generally, foodstuff casings are made either of natural material such as cellulose or animal guts, or of synthetic material. Usually, the foodstuff is packed into the casing. When smoked products are desired, the encased foodstuff can be further subjected to a smoking process. In a conventional smoking process, the product is suspended in a chamber wherein it is exposed to hot smoke from burning wood. This process has the disadvantage that only natural casings can be used in this process, that is, those obtained from guts, for example, or cellulose or collagen casings which all show a natural permeability to smoke.
A critical point in the preparation and storage of smoked products is that the casings must show different permeabilities depending on the step of the process. A high permeability is needed at high temperatures (typically between 50 and 100° C.) and high humidity, during the smoking process. Once the product is smoked and cooled, it is preferable that the casing acts as a barrier against humidity so the permeability should preferably be low at temperatures less than 50° C., particularly less than 30° C.
Casings made from natural products and/or cellulose can present many disadvantages: they can be expensive; their great permeability to steam can cause significant weight loss from a foodstuff; the product can be unstable due to drying and/or superficial fat oxidation. Also, graying caused by microbial spoiling of the natural casing often appears on casings. The manufacturing process for fibrous and cellulose casings involves emissions of carbon disulfide and hydrogen sulfide to the atmosphere, which can be an environmental concern, or require expensive gas scrubbing systems to minimize emissions.
It can be desirable to have an ionomeric synthetic casing that can be used effectively and efficiently for storage and for a smoking process utilizing liquid smoke.